May 2011

Tibial internal rotation emerges as theme in debate over mechanism of ACL rupture

The usual luminaries were on hand in Monaco to exchange familiar barbs over the relative contributions of knee valgus and knee flexion to anterior cruciate ligament injury, but much of the new research being presented suggests that other kinematic variables may play significant roles as well.

One emerging theme is the importance of tibial internal rotation. Tibial IR is a key component of the complex injury mechanism proposed by researchers from the Oslo Sports Trauma Research Center in a November American Journal of Sports Medicine study based on model-based image-matching technology. Hideyuki Koga, MD, PhD, a researcher from the Tokyo Medical and Dental University who recently completed a stint as a guest researcher in Oslo, presented the study results in Monaco.

Computer models were created based on video images of 10 ACL injuries that occurred in female handball and basketball players. Analysis of the models revealed that injury consistently occurred within 40 msec of initial contact, and that those 40 msec were characterized by valgus motion and tibial internal rotation; however, the direction of tibial rotation reversed after ligament rupture. This may explain why video often appears to show tibial external rotation in conjunction with ACL injury even though tibial ER does not increase ACL strain in cadaver studies.

A case study from the same group, published in the May issue of the Clinical Journal of Sports Medicine, confirmed using more advanced MBIM techniques that valgus and internal rotation occur within 30 msec after initial contact, and that anterior tibial translation occurs between 20 msec and 30 msec after initial contact.

“Valgus and internal rotation are important,” Koga said. “But anterior tibial translation is also an important factor.”

A sophisticated cadaver study from the University of Michigan also identifies tibial internal rotation torque as a significant contributor to ACL injury, in this case considerably more so than knee valgus moment.

Researchers subjected the tibias of 12 cadaveric knees to compound test loads, which included a compression load and flexion moment combined with either an internal tibial torque or a valgus knee moment. The cadaver experiment was designed to simulate a one-foot jump landing.

Normalized peak anteromedial ACL relative strain increased by 30% when subjected to knee valgus loading, but increased by 117% in the presence of internally directed tibial torque, according to Edward Wojtys, MD, professor of orthopaedic surgery and chief of sports medicine at the university, who presented the findings in Monaco.